Combination CVD/ALD method, source and pulse profile modification

ABSTRACT

The present invention relates generally to methods and apparatus for the controlled growing of material on substrates. According to embodiments of the present invention, a precursor feed is controlled in order to provide an optimal pulse profile. This may be accomplished by splitting the feed into two paths. One of the paths is restricted in a continuous manner. The other path is restricted in a periodic manner. The output of the two paths converges at a point prior to entry of the reactor. Therefore, a single precursor source is able to fed precursor in to a reactor under two different conditions, one which can be seen as mimicking ALD conditions and one which can be seen as mimicking CVD conditions. This allows for an otherwise single mode reactor to be operated in a plurality of modes including one or more ALD/CVD combination modes. Additionally, the pulse profile of each pulse can be modified. The pulse profile can be modified to create a low or very low partial pressure pulse profile at the beginning of a pulse.

FIELD OF INVENTION

The present invention relates generally to methods and apparatus for thecontrolled growing of material on substrates. Two common technologies inthe present field are ALD and CVD, each having a plurality of drawbacks.The present invention offers a method and apparatus for combining atleast some of the positive aspects of both ALD and CVD processes.Additionally, the pulse profile of each pulse can be modified. The pulseprofile can be modified to create a low or very low partial pressurepulse profile at the beginning of a pulse.

BACKGROUND OF INVENTION

Thin film deposition is used to build materials by in essence growingmaterial on a surface, commonly a substrate. These materials have manyuses in microelectronics as well as in other fields. Two well known thinfilm deposition techniques are Atomic layer deposition (ALD) andChemical Vapor Deposition (CVD). In each technique, reactants, i.e.precursors often in the form of gasses, are fed into a reactor whichover a period of time forms a desired material.

During normal operation of Atomic Layer Deposition (ALD) reactors, twoor more reactants are alternatingly introduced to the reactor. For idealoperation, the switching of gases in the reactor should be as fast andthorough as possible. This makes ALD inherently slow as purging gasvolumes is slow and difficult.

Chemical Vapor deposition (CVD) is based on the continuous flow of aprecursor/precursors to the reactor. Thus, the growth per minute of CVDis generally higher than that in ALD. Due to different requirements forthe ALD and CVD reactors, a CVD reactor historically cannot typically beeasily used for ALD growth of films successfully.

For example, in typical ALD reactors the gas volume in the reactorshould be as small as possible. In CVD reactors, the accurate anduniform concentration distribution over the substrate is a typicaldesign criterion. For CVD reactors, said accurate and uniformconcentration distribution is more important than the low volumerequired by ALD designed reactors.

Source delivery principles are also very different when comparingtypical ALD and CVD reactors. In ALD reactors, it is desirable for theinjection of a concentrated precursor pulse to occur quickly along withthe subsequent fast and thorough purging of the flow channel. To thecontrary, in CVD, the steady and controllable partial pressure flux fromthe source is the most important design factor.

Because CVD is older than ALD, CVD reactor geometry has been optimizedfor the past several decades and is a considerably mature technology.Therefore, it would be very desirable if current CVD reactors could bemodified to function more, or entirely in an ALD mode.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method of operatinga system having a reactor configured to deposit thin films.

Furthermore, it is an aspect of certain embodiments of the presentinvention to provide a method of selectively operating a system having areactor configured to deposit thin films in at least one of thefollowing modes: ALD mode, CVD mode and ALD/CVD combination mode.

Some precursor chemistries which are used in ALD methods can also worksuccessfully in CVD methods, though the partial pressures of theprecursors in the reactor should be accurately controlled. At least inthese cases it is possible to grow films in a combination mode where theALD/CVD film growth mechanisms take place simultaneously.

Accurately controlling the precursor fed into the reactor, especiallyduring an ALD/CVD combination mode enables certain benefits. One resultis that a relatively higher proportion of the ALD mode leads to betterstep coverage of the film. However, a relatively higher proportion ofthe CVD mode leads generally to higher throughput. As good uniformityand low impurity levels in the films can be achieved with both growthmechanisms, accurately controlling the feed of the precursor allows auser to be able to better control the desired output of the thin filmdeposition process.

In order to effectively and efficiently control the precursor fed into areactor, it is beneficial to have a single reactor inlet for eachprecursor. Additionally, it is most efficient to have a single precursorsource for each precursor. However, when operating in an ALD/CVDcombination mode, at least one precursor will need to be fed in to thereactor under different conditions. Therefore, there exists a need for away to effectively and efficiently control a precursor from the timethat it leaves its source until it enters a reactor under at least twodifferent sets of conditions.

According to embodiments of the present invention, a precursor fed issplit in to two paths from the precursor source. One of the paths isrestricted in a continuous manner. The other path is restricted in aperiodic manner. The output of the two paths converges at a point priorto entry of the reactor.

Therefore, according to embodiments of the present invention, a singleprecursor source is able to fed precursor in to the reactor under twodifferent conditions, one mimicking ALD conditions and one mimicking CVDconditions. This allows for an otherwise single mode reactor to beoperated in a plurality of modes including an ALD/CVD combination mode.

Additionally, the pulse profile of each pulse can be modified. The pulseprofile can be modified to create a low or very low concentration pulseprofile at the beginning of a pulse. The pulse profile can be controlledto provide a more uniform reaction which can prevent the creation ofparticles and non-uniform parasitic CVD growth, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general embodiment according to the present inventionshowing a portion of a system 10 having a reactant source vessel 12feeding a reactor 11, wherein the flow of the reactant is controlledcollectively via a 4-way valve and a needle valve.

FIG. 2 shows an embodiment according to the present invention showing aportion of a system 20 similar to FIG. 1, but further showing a secondreactant source vessel 23, wherein the flow of the first reactant iscontrolled collectively via a 4-way valve and a needle valve and whereinthe flow of the second reactant is controlled via a single valve.

FIG. 3 shows an embodiment according to the present invention having areactor 31 fed by two reactant source vessels 32 and 36, wherein theflow of each reactant source vessel is controlled collectively via a4-way valve and a needle valve.

FIG. 4 shows an alternative general embodiment according to the presentinvention showing a portion of a system 40 having a reactant sourcevessel 42 feeding a reactor 41, wherein the flow of the reactant iscontrolled collectively via a plurality of valves.

FIG. 5 shows a schematic of a system 50 according to an embodiment ofthe present invention which is capable of operating a reactor 51 in anALD-CVD combination mode for depositing thin films on a substrate, saidsystem having a plurality of reactant source vessels 52 a-c, wherein theflow from each reactant source vessel to the reactor is controlled via aset of corresponding valves 54 a-c, said sets of valves being controlledby a system controller 56.

FIG. 6 shows pulse profiles created by certain embodiments. Theconcentration of the precursor is controlled such that initially a lowconcentration of precursor is present in the reactor.

FIG. 7 shows an illustration of a partial pressure peak appearingimmediately after opening the valve which supplies the precursor in afast ALD processes, for example one using precursors having usable orsubstantial vapor pressure at room temperature, such as TMA or H₂O, andwith relatively short purge times.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Different applications of thin film technology have different qualityand output requirements for their associated materials. A system whichis capable of growing thin films according to specific needs of acertain application is desirable. It is also desirable to create such asystem which involves the least amount of modification from currentsystems as possible to be able to already refined components.

FIG. 1 shows a portion of a precursor fed arrangement to a reactor 11 ofa system 10 according to an embodiment of the present invention. Inorder to modify an existing system in the least invasive way, it ispreferable to have a single outlet from a precursor source 12 and asingle inlet to a reactor 11 for each precursor. The present embodimentcan be realized as its own system or as a modification of an existingsystem.

As CVD is an older technique compared to ALD, CVD reactor geometries hasbeen optimized over a greater period of time and can be considered morerefined. It is therefore desirable if current CVD reactors can bemodified to function at least partially in the ALD mode. To at leastthat extent, a system including a reactor optimized for CVD operationcan be modified in accordance with the present disclosure. Additionally,the reactor of the present system can be that of an ordinary reactoroptimized for CVD operation.

Examples of suitable reactors can be found at least in U.S. Pat. No.6,562,140, U.S. Pat. No. 6,592,942, U.S. Pat. No. 6,539,891, U.S. Pat.No. 7,020,981 and US Publication 2006/0266289, all of which are hereinincorporated by reference. Furthermore, examples of precursor sourceconfigurations can be found at least in U.S. Pat. No. 6,699,524, U.S.Pat. No. 6,981,517, US Publication 2010/0266765, US Publication2008/0085226 and US Publication 2005/0000428 which are hereinincorporated by reference.

Although, for at least the reasons stated above, it is desirable for thereactor described herein to be one optimized or designed for CVDoperation, the present embodiments can also utilize a reactor optimizedor designed for ALD or other compatible operation. During deposition,the reactor should have one or more substrates positioned inside thereaction chamber. Similarly, the present embodiments can be realized asmodifications to systems including at least one precursor and a reactorwhich is not optimized for CVD, such as ALD or other compatibleoperation.

Retuning to FIG. 1, a precursor or reactant can flow from a precursorsource 12 to a reactor 11 via two paths. The two paths split at point13, a first which can be continuously restricted via a valve 18 and asecond which is controlled by valve 14. In FIG. 1, both paths convergeat a four-way valve 14, 15, 16, 17 and continue from 17 in a single pathto the reactor 11.

During operation of a system 10 in a CVD mode, valves 14 and 15 areclosed, valves 16 and 17 are open and valve 18 restricts the flow of theprecursor from the precursor source 12 to the reactor 11 in a continuousmanner according to CVD conditions. In particular, valve 18 regulatesthe partial pressure of the precursor entering the reactor 11. Valve 18can be a needle valve, a mass flow controller or any other suitableregulator.

The placement of valve 18 can be anywhere along the first path. Thefirst path can start at the point 13 where the first and second pathsdiverge. Alternatively, there can be two outlets from the precursorsource, one for each of the first and second paths. Similarly, it ispreferable that the first path ends at the point where the first andsecond paths rejoin prior to entry of the reactor space, e.g. the fourway valve of FIG. 1.

During operation of a system 10 in an ALD mode, at least one of valves16 and 18 are closed for the duration of operation. In order to avoidany undesirable back flow, it is preferable that at least valve 16remains closed for the duration of operation in the ALD mode. At leastone valve 14 is located along a second path which is capable ofsubstantially and/or completely restricting the flow of the precursor tothe reactor 11. In the present embodiment, said valve 14 is a portion ofa four-way valve which further includes valve 15 which controls the flowa purge gas.

With valve 16 closed the remaining active portion of the systemfunctions according to normal ALD operation. Precursor is admitted pastvalve 14 and 17 in to the reactor 11 for a predetermined amount of timeuntil the flow is ceased, or substantially ceased, via valve 14 so thatthe purge gas from valve 15 can flow through 17 and in to the reactor 11for a second predetermined amount of time.

Therefore, at least through the control of the four way valve, a portionof a system in accordance with FIG. 1 having a precursor source with asingle outlet and a reactor with a single inlet, can selectively beoperated in an ALD or a CVD mode. Additionally, the present system canselectively operate in a combination ALD/CVD mode.

During operation of a system in a combination ALD/CVD mode, precursorfrom both the first and second paths enters the reaction space. In anembodiment according to the present invention, during operation in acombination ALD/CVD mode, valve 16, or the combination of valves 16 and17, allows a continuous amount of precursor from the first path to enterthe reactor 11. The continuous amount of precursor from the first pathis determined and controlled by valve 18.

Simultaneously, valves 14 and 15 operate similar to a standard ALDprocess. An amount of precursor is allowed through valve 14 for a firstpredetermined amount of time before the valve is close. Then an amountof purge gas flows through valve 15 for a second predetermined amount oftime. In some instances, a small amount of precursor can be allowed to“bleed” through valve 14 while the valve is substantially closed, forexample to avoid high pressure buildup behind valve 14.

Therefore, there is always at least the amount of precursor from thefirst path which is able to enter the reactor 11 from the precursorsource 12. The remainder of the material entering the reactor from theinlet is alternatingly made up of the additional precursor from thesecond path and the purge gas. The control of the portion of the system,e.g. the control of the valves, the timing of the valves, the amount ofprecursor that enters the reactor at any given time, can all be chosenor controlled to achieve the desired characteristics of the desiredmaterial and growth process.

In another method of operation, valve 16 is only opened when valve 14 isclosed. Therefore, there is only precursor from one path entering thereactor at any given time, though there is always some of the precursorentering the reactor.

An important characteristic to control during operation of a system inCVD or ALD/CVD combination mode is the partial pressures of precursorsin the reactor. While several portions of the system can be used tomonitor or regulate the total partial pressure of a precursor in areactor either separately or in combination, e.g. 14, 15, 16, 17, anadvantage of the present system and method of operation is that valve 18can regulate the partial pressure of the precursor from precursor source12 during the entire operation in CVD or ALD/CVD combination mode.

During actual operation, control of valve 18 can properly maintain thedesired partial pressure of precursor in the reactor. However,preferably before operation, a user can select the proportion of ALD andCVD mode which is to be used during operation. For example, if good stepcoverage of the film is desired then more ALD mode can be chosen. Insuch an example, the average amount of precursor from the first path islimited so that more growth in the reactor is caused by the pulsedprecursor from the second path then from the continual precursor fromthe first path.

If quick production is desired, then more CVD mode can be chosen. Insuch an example, the average amount of precursor from the first path canbe larger so that there is more growth in the reactor from the continualprecursor from the first path. One of ordinary skill in the art willrecognize a plurality of ways in which the present system can becontrolled to provide desired growth characteristics within a reactor ofthe system operating in a combination ALD/CVD mode having two precursorpaths for a precursor. In many applications of thin film depositionmultiple precursors are required. FIG. 2 shows an embodiment of thepresent invention with a system 20 having two precursor sources 22 and23 feeding to a single reactor 21. In certain applications, one of twoor more precursors is required in greater amounts than the other(s). Inthese applications, one precursor source can operate in an ALD/CVDcombination mode while the other operates in only an ALD mode. In FIG.2, the precursor source 22 is part of a similar arrangement as describedwith regards to FIG. 1. Precursor source 23 is part of a standard ALDarrangement having a control valve 27 having a valve 28 for controllinga purge gas.

The operation of the arrangement of valves 24, having a valve 25 forcontrolling a purge gas, and 26 is similar to that described above withregards to valves 14-18. In the arrangement of system 20, precursorsource 22 will be the precursor source for the precursor which is neededin greatest quantity for the deposition process. Examples of someprocesses which can utilize or be enhanced by the present invention canbe found at least in U.S. Pat. No. 7,732,350, US Publication2008/0317972 and US Publication 2008/0003838 which are hereinincorporated by reference.

An example of a use for system 20 is for the formation of Titaniumnitride (TiN) films in a reactor. Two precursors which can be used toform TiN films are ammonia (NH₃) and titanium chloride (TiCl₄). In orderto increase output, the precursor of precursor source 22 is ammonia andthe precursor of precursor source 23 is titanium chloride. In a normalALD operation mode, ammonia from 22 and titanium chloride from 23 isalternatingly pulsed in to the reactor 21. In between each pulse thelast precursor is purged via its respective purge gas from either 25 or28 prior to the next precursor pulse.

During operation of system 20 in an ALD/CVD combination mode, ammoniafrom 23 can flow in to the reactor 21 during the ammonia purge stepthrough the first path which is controlled by valve 26. In this manner,the amount of ammonia which enters the reactor can increase in the sametime interval which is required during ALD operation. This allows eithermore TiN to form in the same given time, or it allows for the pulse timefor ammonia to decrease allowing for shorter overall process time.

The present arrangement of system 20 allows for numerous precursorcontrol scenarios. For instance, ammonia can be allowed to flow from thefirst path in to the reactor through valve 26 and/or 24 during one ormore of: the ammonia purge step, the entire ammonia pulse step, some orall of the titanium chloride pulse step and in between some or all ofthe pulse steps. Valve 26, 24 or the combination of valves 26 and 24 canregulate the amount and pressure of ammonia entering the reactor in acontinuous, or discontinuous manner as appropriate based on when in theprocess ammonia from the first path is desired to be entered into thereactor.

Although the present example is directed to the formation of titaniumnitride from two precursors, ammonia and titanium chloride, the systemand method of operation can be used for various other chemicaldepositions. FIG. 3 shows a system 30 which has a reactor 31, twoprecursor sources 32 and 36, each precursor source having an arrangementof paths and valves 33-35 and 37-39 respectively which can be arrangedand operate as discussed above. System 30 can be operated as wasdescribed in the titanium nitride example above with ammonia in either32 or 36 and with titanium chloride in the other source. The valvearrangements connected to the titanium chloride precursor source wouldthen operate only in an ALD mode while the valve arrangements connectedto the ammonia source would operate in an ALD/CVD combination mode asdescribed.

Therefore, in a system having multiple precursor sources connected to areactor in an arrangement as described for instance in FIG. 1, eachprecursor source arrangement can be independently selectively operatedin an ALD mode, CVD mode, ALD/CVD combination mode or an off mode if itis not required in a particular deposition. Generally, one or more ofthe precursors in a system as described herein can comprise a transitionmetal. Some examples of transition metals, specifically transition metalhalides, which can be used in the present systems are TiCl₄, WF₆, TaCl₅,TaF₅, MoF_(x), ZrCl₄ or HfCl₄. In some cases, one or more of theprecursors in a system as described herein can comprises silicon, whichmay be preferably silicon halide, for example SiCl₄, or a siliconcompound with organic ligands, which may be preferably aminoligands, forexample bis(dimethylamino)silane, bis(diethylamino)silane,bis(ethylmethylamino)silane, di-isopropylaminosilane and/orhexakis(ethylamino)disilane. Additionally, examples of other reactantswhich can be used with the aforementioned transition metals, alone orwith other reactants are NH₃, H₂O, O₂ and O₃ Plasmas and radicalscontaining nitrogen, oxygen or hydrogen species can also be used asother reactants.

FIG. 4 shows an alternative arrangement of valves in a portion of asystem 40, similar to that of FIG. 1, but without a four way valve. InFIG. 4, precursor from the precursor source 42 can flow to the reactor41 via a first and second path. The two paths diverge at point 43 andrejoin at point 49 prior to entry to the reactor 41. Prior to the pointof rejoinder 49, each path has its own valve which controls the outputof the path, 48 for the first path and 44/46 for the second path. Thefirst path includes a valve 47 and the second path includes a valve 45for controlling a purge gas, both as previously described.

Locations 43 and 49 can be virtually anywhere along the overall pathbetween the precursor source 42 and reactor 41. As discussed above, itis preferable that there is only one outlet from the precursor sourceand one inlet to the reactor for each precursor. However, it isconceivable that there are two outlets from the precursor source (notshown), one dedicated to each path. Additionally, in order to avoidunnecessary dead space in the system, it is desirable to locate point 49as close to valves 44-46, an optimal location being at a four way valve.

FIG. 5 shows an example of a system 50 having a plurality of precursorsources 52 a-c, each precursor source having an arrangement of valves 54a-c. Each of the arrangement of valves can include multiple paths asshown in solid lines for 54 a allowing for the precursor sourcearrangement to operate in an ALD/CVD combination mode. In an embodiment,all of the arrangements 54 a-c are similar or identical and are inaccordance with the arrangements discussed with regards to FIGS. 1 and4. In said embodiment, all of the arrangements 54 a-c can be operatedselectively in either an ALD mode, CVD mode, ALD/CVD combination mode oran off mode if not all of the arrangements are necessary. In anotherembodiment, only some of the arrangements are in accordance with thearrangements for ALD/CVD combination mode, 54 a. The other arrangements54 b and 54 c can be fixed ALD, CVD or other arrangements. In such anembodiment, any or all of the arrangements 54 a-c can be operated in afixed mode, i.e. where the operation mode is not selectable.

The system 50 is controlled by at least one controller 56. Controller 56can be a processor, CPU, server, mainframe or other suitable controlleror device which is capable of controlling the flow of precursors fromtheir respective precursor sources 52 a-c to the reactor 51 via theirrespective valve arrangements 54 a-c.

FIG. 6 shows pulse profiles created by certain embodiments. The partialpressure or partial pressure profile of the precursor is controlled suchthat initially a low partial pressure of precursor is present in thereactor. Partial pressure in this context can also be understood tocomprise concentration.

In fast ALD processing using precursors having usable or substantialvapor pressure at room temperature, such as TMA or H₂O, and withrelatively short purge times, a partial pressure peak often appearsimmediately after opening the valve which supplies the precursor. Thisis illustrated as an example in FIG. 7. This partial pressure peak inthe precursor pulse can react with a previous precursor pulse tail, orremainings, left after purging in the reaction space. This reaction cancause high partial pressures of precursor in the reaction space thuscausing a high partial pressure precursor pulse. The amount of precursorentering the reaction space corresponds or is proportional to thepartial pressure of the precursor multiplied by the time in which theprecursor is entering the reaction space. This is illustrated withshadings 71 and 72 in FIG. 7. The areas of 71 and 72 are proportional tothe amount of precursor entering the reaction chamber. For simplicitythe shaded areas are drawn as rectangles illustrating the maximum amountof precursor entering the reaction space (e.g. the maximum vaporpressure times time). Another possibility is to follow the partialpressure, although in practice, depending on: measurement errors,measurement frequency/accuracy, measurement location or a combinationthereof, the partial pressure curve shape and the shaded area mightvary. FIG. 7 is merely an illustration, of arbitrary proportionalamounts of precursor after the valve is opened in a fixed time. The timein both FIGS. 6 and 7 is the same and is roughly 2 seconds (e.g. thewidth of the shaded area rectangle).

These high partial pressure precursor pulses can cause particleformation and non-uniform parasitic CVD growth. This can be especiallyprevalent if a high partial pressure is occurring at the beginning ofpulse and/or if there is a partial pressure peak in the beginning ofpulse. Through modification of the partial pressure of the precursorsupplied over time, and/or the pulse profile, particularly at thebeginning of a pulse, better control over partial pressures of precursorwithin the reaction space can be achieved.

FIG. 6 shows an example of pulse profiles modified as discussed herein.An example of a pulse profile modification is that at first, a very lowpartial pressure pulse is introduced to the reaction space. The pulseprofile of each pulse of reactant entering a reaction space can includeless than half of the total amount of precursor within the first half ofthe pulse. By example, less than 50% or about 50% of the total amount ofprecursor in one pulse can be introduced to the reaction space duringthe first half, or about the first half of the pulse length. Accordingto certain examples, very low partial pressure pulse can be less than30%, 20% or even less than 10% of the total amount of precursor in apulse is introduced to the reaction space during the first half of thepulse length.

Pulse length can be determined as the actual or nominal pulse length,e.g. the time from opening the precursor valve to the time of closingthe valve to precursor vessel.

Furthermore, a very low partial pressure pulse profile can also berealized as less than 25% or about 25%, of the total amount of precursorin the pulse is introduced to the reaction space during the firstquarter (25%) of the pulse length. According to certain examples, thepartial pressure can be even lower, e.g. less than 20%, 10% or even lessthan 5% of the total amount of precursor in the one pulse can beintroduced to the reaction space during the first quarter of the pulselength.

According certain embodiments, a very low partial pressure pulse profilecan also be realized as providing partial pressure having maximum ofless than 25% or about 25%, of the highest partial pressure within thepulse to the reaction space during the first quarter (25%) of the pulselength. According to certain examples, the maximum partial pressureintroduced to the reaction space during the first quarter of the pulselength can be even lower, e.g. less than 20%, 10% or even less than 5%of the highest partial pressure within the one pulse. According certainother embodiments, a very low partial pressure pulse profile can also berealized as providing partial pressure having maximum of less than 50%or about 50%, of the highest partial pressure within the pulse to thereaction space during the first half (50%) of the pulse length.According to certain examples, the maximum partial pressure introducedto the reaction space during the first half of the pulse length can beeven lower, e.g. less than 30%, 20% or even less than 10% of the highestpartial pressure within the one pulse. Furthermore, a very low dosagepulse profile can also be realized as less than 25% or about 25%, of thetotal amount of precursor in the pulse is introduced to the reactionspace during the first quarter (25%) of the pulse length. According tocertain examples, the dosage can be even lower, e.g. less than 20%, 10%or even less than 5% of the total amount of precursor in the one pulsecan be introduced to the reaction space during the first quarter of thepulse length. In yet another embodiment a very low dosage pulse profilecan also be realized as less than 50% or about 50%, of the total amountof precursor in the pulse is introduced to the reaction space during thehalf (50%) of the pulse length. According to certain examples, thedosage can be even lower, e.g. less than 30%, 20% or even less than 10%of the total amount of precursor in the one pulse can be introduced tothe reaction space during the first half of the pulse length.

Following a very low partial pressure pulse introduction, a higherpartial pressure pulse profile can be introduced, for example asillustrated by pulse profile 61 (the shaded area a). A further exampleof pulse profile modification is a pulse profile with a decreasingpartial pressure as illustrated in pulse profile 62 (the shaded area b).

According certain embodiments, less than 50%, less than about 30%, lessthan about 20% or less than about 10% of the total amount of precursorin the one pulse is introduced to the reaction space in less than aboutthe first 0.2 seconds of a precursor pulse, in less than about the first0.5 seconds of precursor pulse or in less than about the first 1.0second of precursor pulse. According to certain embodiments, less than25%, less than about 20%, less than about 10% or less than about 5% ofthe total amount of precursor in one pulse is introduced to the reactionspace in less than about the first 0.1 seconds of precursor pulse, inless than about the first 0.5 seconds of precursor pulse or in less thanabout the first 1.0 second of the precursor pulse.

Precursor pulse profiles provided herein provide for low partialpressure precursor pulses, e.g. precursor pulses having a lower partialpressure in the first quarter or half of the pulse compared to theremaining portion of the pulse. These low partial pressure precursorpulses allow for a more uniform reaction in the different sections ofthe reaction chamber. A more uniform reaction exhibits a lower growthrate with less gas phase reactions and particles. Such a uniformreaction can prevent the creation of particles and non-uniform parasiticCVD growth.

In a method of operating a system having a reactor configured to depositthin films, amounts of reactants provided can be controlled. First, anamount of reactant from a reactant source vessel can be provided to areaction space at a first volumetric flow rate. Subsequent to providingthe first amount of reactant to the reaction space, a second amount ofthe reactant is provided to the reaction space at a second volumetricflow rate. The second volumetric flow rate should be greater than thefirst volumetric flow rate. The second amount of the reactant may be,but is not necessarily, sourced from the same reactant source vessel asthe first amount.

After the second amount of the reactant is provided to the reactionspace the reactant can be removed from the reaction space. Furthermore,the steps of: providing the first amount of reactant, subsequentlyproviding the second amount of reactant and removing the reactant, canbe performed sequentially and they can be performed multiple times,preferably in the mentioned order.

According to certain embodiments, the system having a reactor configuredto deposit thin films is and/or is for performing an ALD process. Insome embodiments, the average of the first volumetric flow rate duringproviding the first amount of reactant is less than about 75%, less thanabout 50%, less than about 30% or less than about 10% of the average ofthe second volumetric flow rate during the time of providing the secondamount of reactant. The length or time of providing the first amount ofreactant can be less than about 100%, less than about 50%, less thanabout 30% or less than about 20%, and in some cases can be less thanabout 10% of the corresponding length or time of providing the secondamount of reactant.

As mentioned above it is desirable to control the partial pressure ofprecursor present in the reaction space over time and create an optimalprecursor pulse profile. For example, to form a pulse profile in amethod as discussed herein, the first amount of reactant can be limitedto at most a predetermined percentage of the second amount of reactant.The timing of the first and second amount may also be controlled inorder to optimize the pulse profiles. For example, to form a pulseprofile in a method as discussed herein, the second amount can beprovided at least a predetermined seconds or portion thereof after theinitiation of providing the first amount. Furthermore a pulse profilecould be constructed according to the method as discussed herein suchthat the first amount continues to flow at the same first flow rateafter providing the second amount has been initiated. The pulse profilemay also be such that the first amount is continuously provided to thereaction space.

The system of FIG. 1 may be used to implement the methods discussedherein. A precursor or reactant can flow from a precursor source 12 to areactor 11 via two paths. The two paths split at point 13, a first whichpasses through valve 18 to valve 16 and a second which is controlled byvalve 14. The first path can be periodically substantially restricted byvalve 16. The first path can also be continuously restricted by valve18. The second path can be periodically substantially restricted byvalve 14. In FIG. 1, both paths converge at a four-way valve 14, 15, 16,17 and continue from 17 in a single path to the reactor 11. The valve 16which substantially restricts the flow of the first path may be operatedsuch that when the second path is substantially restricted, there is noflow of reactant from the second path entering the reaction space. Thesystem 10 of FIG. 1 operated in accordance with the methods describedherein can allow for greater control and modification of the pulseprofile which can avoid the creation of particles and promote uniformreaction.

The pulse profile, e.g. as shown as 62 in FIG. 6, can also be controlledaccurately by, for example, using a mass flow controller (MFC),connected to a source line and ramping up the flow rate in desiredmanner accurately. The MFC can be controlled by a computer, processor orcontroller. Furthermore, with a computer controlled MCF the desiredpulse profile can be achieved, programmed, pre-programmed and/orcontrolled.

It is to be understood that the embodiments of the invention disclosedare not limited to the particular structures, process steps, ormaterials disclosed herein, but are extended to equivalents thereof aswould be recognized by those ordinarily skilled in the relevant arts. Itshould also be understood that terminology employed herein is used forthe purpose of describing particular embodiments only and is notintended to be limiting.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as de factoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of lengths, widths, shapes, etc., to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

1-20. (canceled)
 21. A method of depositing a thin film on a substratecomprising: delivering a plurality of pulsed flows of a reactant atspaced apart time intervals to a reaction space of a reaction vessel todeposit the thin film on the substrate, each pulsed flow having a pulsetime duration, between selected pulsed flows of the plurality of pulsedflows, delivering a purge gas to the reaction space to remove thereactant from the reaction space, and wherein each pulsed flow deliveredto the reaction space includes less than 25% of a concentration of thereactant for the pulsed flow within a first 25% of the pulse timeduration.
 22. The method of claim 21, wherein the concentrationcomprises a partial pressure of the reactant.
 23. The method of claim21, wherein each pulsed flow delivered to the reaction space includesless than 20% of the concentration of the reactant for the pulsed flowwithin the first 25% of the pulse time duration.
 24. The method of claim21, wherein each pulsed flow delivered to the reaction space includesless than 10% of the concentration of the reactant for the pulsed flowwithin the first 25% of the pulse time duration.
 25. The method of claim21, wherein each pulsed flow delivered to the reaction space includesless than 5% of the concentration of the reactant for the pulsed flowwithin the first 25% of the pulse time duration.
 26. The methodaccording to claim 21, wherein the substrate comprises a silicon wafer.27. The method according to claim 21, further comprising delivering asecond reactant distinct from the first reactant to the reaction space28. The method according to claim 27, wherein the second reactant isdelivered continuously to the reaction space.
 29. The method accordingto claim 21, wherein the first half of the pulse time duration is 1.0second or less, and wherein each pulsed flow of the reactant enteringthe reaction space includes less than the 25% of the second reactantwithin the 1.0 second or less.
 30. A system for depositing a thin filmon a substrate comprising: a reactor comprising a reaction space; areactant source in fluid communication with the reactor via a fluidpath, wherein the fluid path comprises a valve operable to deliver aplurality of pulsed flows of the reactant at spaced apart time intervalsto the reaction space to deposit the thin film on the substrate, whereineach pulsed flow has a pulse time duration, and wherein each pulsed flowdelivered to the reaction space includes less than 25% of aconcentration of the reactant for the pulsed flow within a first 25% ofthe pulse time duration; and a source of a purge gas further in fluidcommunication with the reaction space via the valve, wherein the valveis also configured to restrict or cease flow of the reactant and delivera purge gas to the reaction space to remove the reactant from thereaction space between selected pulsed flows of the plurality of pulsedflows.
 31. The system of claim 30, wherein the concentration comprises apartial pressure of the reactant.
 32. The system of claim 30, whereineach pulsed flow delivered to the reaction space includes less than 20%of the concentration of the reactant for the pulsed flow within thefirst 25% of the pulse time duration.
 33. The system of claim 30,wherein each pulsed flow delivered to the reaction space includes lessthan 10% of the concentration of the reactant for the pulsed flow withinthe first 25% of the pulse time duration.
 34. The system of claim 30,wherein each pulsed flow entering the reaction space includes less than5% of the concentration of the reactant for the pulsed flow within thefirst 25% of the pulse time duration.
 35. The system of claim 30,wherein the substrate comprises a silicon wafer.
 36. The system of claim30, further comprising a source of a second reactant in fluidcommunication with the reaction space, and wherein the valve is furtheroperable to deliver the second reactant to the reaction space.